Coaxial directional couplers are known, such as disclosed, for example, in U.S. Pat. No. 2,657,361 and 3,358,248. However, known coaxial directional couplers are relatively expensive to produce due to their structure and the fact that their physical dimensions must be changed with different operating applications of the coupler. The most common type of coupler in the field of this invention utilizes solid stripline construction techniques. In such techniques it is required, as shown for example in U.S. Pat. No. 4,547,753, to couple the coaxial cables within a machined metal housing or other form of housing for shielding, and the housing is then filled with a sealant, such as epoxy, in order to make the unit impervious to humidity and other environmental hazards. Accordingly, known couplers are expensive to fabricate as the manufacturing process is relatively lengthy as well as the design time.
A further disadvantage of some of these coupler designs is that their size can be fairly large depending on their frequency coupling, and cannot be fitted in restrained spaces. They do not offer flexibility.